How do cucumber leaves respond to fruiting?

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Dai et al. demonstrate the key function of a non-coding RNA delicately regulating cucumber fruit–leaf relationship

By The research group led by Prof. Minmin Miao from Yangzhou University

Background: For fruit-bearing crops, plants must allocate photosynthate from leaves to fruits. Most fruiting plants mainly transport sucrose from leaves to other organs. However, stachyose is the main sugar that is transported in cucumber. The enzyme stachyose synthase (CsSTS) synthesizes stachyose in mesophyll and vascular tissues and is considered a key regulator of carbon partitioning. To date, we know little about the fruit-leaf regulation mechanism of stachyose-transporting species. In addition, long non-coding RNAs (lncRNAs) are RNAs longer than 200 base pairs that have no protein coding potential but may regulate gene expression. An LncRNA of CsSTS, named asCsSTS, is mainly expressed in cucumber mesophyll tissues.

Question: Does the asCsSTS lncRNA play a role in cucumber fruit-leaf interactions by regulating CsSTS expression?

Findings: Through a series of experiments, we confirmed that asCsSTS interacts and negatively regulates CsSTS abundance by reducing CsSTS RNA stability in cucumber mesophyll tissues. When the cucumber plant carries fruit, asCsSTS expression increases while CsSTS transcript abundance decreases in mesophyll tissues of the leaf at the fruiting-node. At the same time, another unknown mechanism up-regulates CsSTS expression in vascular tissues. This synergetic regulation reduces sugar storage in mesophyll tissues and promotes sugar export from the leaf through loading into the vasculature, and then accelerates fruit growth. The results provide useful information to improve cucumber yield by altering the fruit-leaf relationship.

Next steps: We would like to further investigate how cucumber leaves know there is a fruit. The role of sugar signaling in long-distance communication between different organs in a plant is well established. We guess the signal transduced from fruit to leaf in this study is also a sugar, such as sucrose, hexose, or stachyose.

Reference:

Haibo Dai, Wenyan Zhang, Bing Hua, Zihui Zhu, Jinji Zhang, Zhiping Zhang, Minmin Miao. (2023). Cucumber STACHYOSE SYNTHASE is regulated by its cis-antisense RNA asCsSTS to balance source–sink carbon partitioning. https://doi.org/10.1093/plcell/koac317